Ultra-Wideband Antenna Design for
Transmission of a Digital Chaotic Signal
S.D. Cohen, H.L.D. de S. Cavalcante, R. Zhang, D.J. Gauthier
Department of Physics, Duke University
Antenna Design
Introduction: The transfer of information
between chaotic elements is of great interest
in understanding the dynamics of large
coupled
networks.
To
explore
the
synchronization characterizations of such a
network, we have begun examining methods
for radio frequency signal transmission
between chaotic oscillators. Coupling
through radio transmission, rather than hardwire connections, will allow for additional
elements to be more easily added into the
network. The individual oscillators are
realized using a design with high-speed,
commercially available logic gates that feed
back to each other with independent delays.
Each circuit operates in the ultra-highfrequency portion of the electromagnetic
spectrum and satisfies the ultra-wide-band
(UWB) criterion for a telecommunication
device [1].
Transmitted Power Spectrum ( 1 m)
Modulation / Recovery
Ultra-Wideband (UWB):
A signal occupying over 500 MHz of the
frequency spectrum. Or, a signal of fractional
bandwidth Bf > 0.2, Bf = 2 (fH - fL) / (fH + fL) [2].
FH = upper frequency of -10 dB,
FL = lower frequency of -10 dB.
Motivation:
• Design an antenna that transmits and recovers
the information of such a digital chaotic device.
Frequency Shift via Phase Modulation:
1) Make two inverted copies of the
chaotic signal.
2) I/Q mod. mixes each copy with a local
oscillator (LO) of opposite phase
(frequency 1400 MHz) and sums.
3) State transitions in the digital logic
correspond to phase changes in the
analog transmission.
Inverted Copies of Chaotic Signal
1)
• Power concentrated in the antenna's pass-band with unfiltered transmission [4].
First Generation Design:
• I/Q demodulator recovers the primary components of the digital signal.
• Copper-trace monopole antenna printed on
80 mm x 150 mm FR4 dielectric.
• Recovered waveform is filtered, biased, and reintegrated into a digital logic gate
(Note: some short pulses are lost in transmission).
2)
Recovery of Transmitted Chaotic Signal
Raw Transmission
Chaotic Spectrum:
Digital Chaotic Frequency Spectrum
3)
• Digital chaos has an
UWB bandwidth from
30 MHz – 2.5 GHz.
=
• Antenna efficiency
pass-band runs from
800 MHz – 2 GHz
(covering only a portion
of
the
oscillator's
bandwidth) [3].
Problem:
Phase Modulated Chaotic Signal
Circuit Schematic 1.
Raw Close Range Transmission ( < 1 cm )
Conclusions: Modulation aligns the chaotic frequency distribution within
the first generation UWB antenna’s pass-band, allowing for unfiltered
transmission. A demodulation technique has been designed to
successfully recover the transmitted chaotic signal. This transfer of
information will be used to couple two or more of these elements in an
area for further study.
Simulated Chaotic Frequency Shift
• Transmission filtered
by antenna’s pass-band.
•
At distances larger
than 1 cm, oscillations
from
filtering
have
amplitudes comparable
to signal.
Chaotic Transmitter
Circuit Schematic 2.
Chaotic Receiver
Future Work
• Use the recovered signal to drive a coupled circuit.
• Incorporate a circulator for simultaneous transmission / recovery.
• Shift to FCC bandwidth (3.1-10.6 GHz) with modulation / smaller antenna.
Solution:
• Shift spectrum of signal
within antenna's passband.
References
1 - Posters given by H.L.D. De S. Cavalcante (P62) and R. Zhang (P72).
2 - Federal Communications Commission FCC02-48
3 - IE3D Software Release 4.0, Zeland Software Inc., Fremont, California, USA.
4 – UWB Test Report, Mlinarsky and Ziegler, www.octoscope.com, ( 2007)